State profile · EPA SDWIS + UCMR5
Delaware Drinking Water Quality
460 systems serve 1,083,630. Health-based share of the violation record is 50%; SDWIS systems with ≥1 violation: 74.8%.
- 460
- SDWIS water systems
- 9,105
- Total violations
- 74.8%
- SDWIS systems w/ a violation
- 48.6%
- UCMR5 PFAS rate (35 tested)
The verdict
50% of 9,105 recorded violations are health-based across 460 systems. According to EPA SDWIS population served, Delaware ranks #45 of 66 states and territories by people served through public water systems.
- #45 of 66
- Population · states corpus
- 9,105
- Total EPA violations on record
- 50%
- Health-based (MCL / treatment)
- 74.8%
- SDWIS systems with ≥1 violation
SDWIS violation % and UCMR5 PFAS % use different denominators (full inventory vs tested subset). Population ordinal uses SDWIS population served.
Delaware standing, low SDWIS violation-rate third
Delaware is in the lower third of jurisdictions by violation rate (74.8%; lower-third rate (≤ 92.5%)). That is a relative placement among peers, not a claim that most systems are clean - 344 of 460 still carry ≥1 record. Population served is smaller (1,083,630; smaller served population (≤ 1,083,630)), so a high rate can still mean a compact household footprint. Health-based share is 50% - most of this ledger is MCL or treatment-technique exceedance, not paperwork. UCMR5 PFAS detection is 48.6% on the tested subset (upper-third UCMR5 detection (> 35.3%)) - a different denominator from the SDWIS violation rate. Systems listed below are ranked by population served or violation count; pair rate with inventory size before reading exposure scale.
Nationwide similar states
Nearest by SDWIS violation rate
Nearest by population served
Health-based share of this violation record
EPA SDWIS classifications for Delaware's 9,105 recorded violations.
Delaware vs nearest violation-rate peers
Share of SDWIS-listed systems with at least one recorded violation; peers are nearest by absolute rate distance, not a fixed top-seven list.
- DE
Delaware
74.8 % of systems
- WI
Wisconsin
72.1 % of systems
- MD
Maryland
79.9 % of systems
- HI
Hawaii
80.3 % of systems
- IL
Illinois
80.8 % of systems
What this shows Delaware's rate is 74.8% (344 of 460 systems; lower-third rate (≤ 92.5%)). This is a comparison of recorded SDWIS violations, not a measure of current water safety.
Delaware vs all jurisdictions by SDWIS system inventory
Where this state's public water system count sits among every state and territory on PlainWater
460 47th of 66 higher than 19 of 66 jurisdictions
States and territories, banded by SDWIS-listed public water system count
Each bar is a band; taller bars hold more jurisdictions. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count and share, and where it sits relative to this entry.
Source EPA SDWIS state aggregates · 2026-05-15
Largest Water Systems
Most Violations
Counties in Delaware
Context: PFAS in drinking water · methodology · all states
Every figure on PlainWater is rendered directly from EPA SDWIS drinking-water data, no number is typed in by an editor. This page draws directly on EPA SDWIS data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.